first image does not show except in old version of Firefox

I have:
- Colorbox module 7.x-2.12
- Colorbox plugin: 1.6.4

With latest Chrome, IE, Firefox, when i open a colorbox (with a REL grouped set of images, using inline mode), the first slide shows only the faded out background with empty contents. But, if i cycle through the slides with the cursor keys, all the slides after the first one, show correctly (even the first one when i get back to it in the cycle).

Also, i have an older version of Firefox (38), and it works correctly.

Site can be seen here: http://athleteos.liquidcms.org/user/1/album